This invention relates generally to rotary drum spray grainers and more particularly to the use of the air flow in a rotary drum spray grainer to obtain air classification of the spray grained calcium hypochlorite product particles as the particles exit the rotary drum spray grainer passing counter-current to the inlet hot air flow.
The use of a rotary drum apparatus to apply coatings or encapsulations to particulate substrates by the spraying of slurries, melts, or solutions and suspensions onto moving beds of particles that fall in cascades within the apparatus is well known. The application of distinct and separate coatings to a particulate substrate is known as granulation and is widely used in the fertilizer industry, for example in the production of ammonium nitrate. The application of coatings or encapsulations on a particulate substrate can also be employed in the making of confections, such as sugars, or, as in the case of the instant invention, in the manufacture of calcium hypochlorite for use as a commercial bleaching and sanitizing agent, particularly in the disinfection of swimming pool waters.
Previous attempts to employ a rotary drum spray grainer in the process of manufacturing spray grained particles employ either a deflector means that runs the entire length of the rotary drum and which overlies the spraying means or nozzles or, in the alternative, utilize no deflector means in the rotary drum. Both of these approaches utilize spray grainer particle flow that is in the same direction as or co-current to the direction of inlet air flow into the drum. In other words, inlet air is brought in a first end of the drum and the spray grained product particles exit the opposing second end of the drum. Seed particles are also normally introduced at or near the first end of the drum.
Rotary drum spray grainers which use this co-current product particle flow in the same direction as the air flow through the drum require some type of an external sorting and recycle of the undersized product particles by a screw type of conveyor back into the spray grainer. This movement of the product particles outside of the spray grainer frequently can cause excessive cracking or crumbling of the undersized particles due to the increased movement. The shape of the finished product in this type of a system will also be irregular and not generally round.
These disadvantages are solved in the design of the present invention by providing a classification zone at or adjacent the first end of the rotary drum spray grainer through which the product particles pass in a direction counter-current to the flow of inlet air as the product particles exit the rotary drum spray grainer.